Our three-year collaboration with ARK Rewilding Netherlands had this goal: to test the potential of rewilding principles in restoring ocean biodiversity as we speed up the global transition to renewable energy.
Now in our second year of the project, we are actively restoring biogenic reefs and monitoring the effects at two sites in the Dutch North Sea: the Voordelta, in subtidal waters, and Borkum Stones, further offshore. The North Sea is one of the most human-impacted seas in the world.
Rewilding involves taking an ecosystem-wide view and creating conditions in which nature can recover and thrive on its own, over the long-term. Key principles of rewilding include establishing core areas for natural regeneration, ensuring connectivity (movement/migration) between those core areas and promoting the recovery of predators and other keystone species – species that have a strong influence on the function of the ecosystem.
The approach has never before been trialed at scale in the marine environment, where the challenge is particularly acute, but where ARK and Ørsted believe there is huge potential benefit.
ARK and Ørsted have a shared vision: as the offshore wind needed to tackle the climate challenge takes up more marine space, we must work together to leave nature in better shape than we found it.
The principles of marine rewilding showing the intervention and potential outcome
We’ve set up a Marine Field Lab for rewilding in the North Sea. We’re focusing on:
Just one century ago, European flat oysters covered one-fifth of the Dutch part of the North Sea, but the species has been almost lost owing to fisheries, disease, and pollution. Currently there are very few places remaining in the North Sea where oyster larvae can attach and create new reefs.
How are we catalysing the recovery of the European flat oyster?
Collecting adult oysters to produce oyster larvae
First, we collect adult oysters from Oosterschelde – the eastern estuary of the Schelde which flows into Voordelta. The collected oysters are used as a broodstock in a hatchery. The broodstock is used to produce oyster larvae.
Placing the oysters on old shells
After around two weeks the oyster larvae change into ‘spats’. At this stage we place the small oysters, now juveniles, on old shells at our restoration sites. The old shells come from France. In 2025 the first local shells will be used in this project, as we are working on a system to collect oyster shells from Dutch restaurants project called Help With Shells.
Deploying the spat-on-shell at the test sites
Once the spat-on-shell has grown strong enough, after two to three weeks, it is deployed at the test sites. This is done with protected cages, called oyster cradles. The oyster cradles are designed to protect the oysters from the harsh conditions of the North Sea and predators until they have grown into adults and are reproducing. At that stage, the cradles will have deteriorated.
So far, we have deployed 15m3 of spat-on-shell at the two sites, Voordelta and Borkum Stones. Results from monitoring will help us understand the growth, survival and reproduction of the oysters. Monitoring will also help us determine how to upscale the cradle for application in a larger seascape. Broader ecological effects and success of the recovery of the reef can be measured at a later stage.
